A known image forming apparatus includes a main body defining a sheet conveying path in which a recording sheet is conveyed, and a photosensitive member unit including a plurality of photosensitive members corresponding to respective colors. The photosensitive members are arranged in line or tandem with respect to the sheet conveying path. The image forming apparatus is of an electrophotographic type in which a color image is formed on a recording sheet by transferring toner images carried on the photosensitive drums onto a surface of the recording sheet conveyed in the sheet conveying path.
The photosensitive member unit is attachable to the main body by moving along a placement path between a position where the photosensitive member unit is removable outside the main body and an operational position where an image is ready to be formed in the main body. The photosensitive member unit is detachable from the main body by moving along the placement path in an opposite direction to an attachment direction.
The main body includes a force transmitting device that is configured to transmit a drive force from outside the main body in a width direction perpendicular to the sheet conveying path to the photosensitive member unit placed in the operational position. The photosensitive member unit includes a force receiving device, which is configured to engage the force transmitting device and receive a drive force from the force transmitting device when the photosensitive member unit is in the operational position.
The main body further includes: a contact surface that contacts, from below rearward, a positioning shaft protruding outward in the width direction from a front part of the photosensitive member unit placed in the operational position; a pressing arm that presses the positioning shaft that contacts the contact surface rearward; and a reference shaft that contacts, from below rearward, a cut portion recessed in a rear end of the photosensitive member unit in the operational position.
In the image forming apparatus, when the photosensitive member unit moves along the placement path and reaches the operational position, the positioning shaft contacts the contact surface, and the pressing arm presses the positioning shaft rearward. Thereby, the cut portion reliably contacts the reference shaft and the photosensitive member unit is positioned in a front-rear direction along the sheet conveying path.